Of Opposition.
§ 449. Opposition is an immediate inference grounded on the relation between propositions which have the same terms, but differ in quantity or in quality or in both.
§ 450. In order that there should be any formal opposition between two propositions, it is necessary that their terms should be the same. There can be no opposition between two such propositions as these—
(1) All angels have wings.
(2) No cows are carnivorous.
§ 451. If we are given a pair of terms, say A for subject and B for predicate, and allowed to affix such quantity and quality as we please, we can of course make up the four kinds of proposition recognised by logic, namely,
A. All A is B.
E. No A is B.
I. Some A is B.
O. Some A is not B.